U.S. patent application number 11/864369 was filed with the patent office on 2011-11-17 for self-assembly of micro-structures.
This patent application is currently assigned to SUN MICROSYSTEMS, INC.. Invention is credited to John E. Cunningham, Ashok V. Krishnamoorthy, James G. Mitchell.
Application Number | 20110281395 11/864369 |
Document ID | / |
Family ID | 40110970 |
Filed Date | 2011-11-17 |
United States Patent
Application |
20110281395 |
Kind Code |
A1 |
Krishnamoorthy; Ashok V. ;
et al. |
November 17, 2011 |
SELF-ASSEMBLY OF MICRO-STRUCTURES
Abstract
Embodiments of a method for assembling a multi-chip module (MCM)
are described. During this method, a fluid that includes coupling
elements is applied to a surface of a base plate in the MCM. Then,
at least some of the coupling elements are positioned into negative
features on the surface of the base plate using fluidic assembly.
Note that a given coupling element selects a given negative feature
using chemical-based selection and/or geometry-based selection.
Next, the fluid and excess coupling elements (which reside in
regions outside of the negative features on the surface) are
removed.
Inventors: |
Krishnamoorthy; Ashok V.;
(San Diego, CA) ; Cunningham; John E.; (San Diego,
CA) ; Mitchell; James G.; (Palo Alto, CA) |
Assignee: |
SUN MICROSYSTEMS, INC.
Santa Clara
CA
|
Family ID: |
40110970 |
Appl. No.: |
11/864369 |
Filed: |
September 28, 2007 |
Current U.S.
Class: |
438/107 ;
257/E21.499 |
Current CPC
Class: |
H01L 25/0657 20130101;
H01L 2924/10253 20130101; H01L 2224/16 20130101; H01L 2225/06593
20130101; H01L 2924/01079 20130101; H01L 2225/06513 20130101; H01L
2225/06534 20130101; H01L 2924/10253 20130101; H01L 2924/00
20130101; H01L 25/50 20130101; H01L 2225/06531 20130101; H01L 23/48
20130101 |
Class at
Publication: |
438/107 ;
257/E21.499 |
International
Class: |
H01L 21/50 20060101
H01L021/50 |
Goverment Interests
GOVERNMENT LICENSE RIGHTS
[0001] This invention was made with United States Government
support under Contract No. NBCH3039002 awarded by the Defense
Advanced Research Projects Administration. The United States
Government has certain rights in the invention.
Claims
1. A method for assembling a multi-chip module (MCM), comprising:
applying a fluid to a surface of a base plate in the MCM, wherein
the fluid includes coupling elements; positioning at least some of
the coupling elements into negative features on the surface of the
base plate using fluidic assembly, wherein a given coupling element
selects a given negative feature using chemical-based selection and
geometry-based selection; and removing the fluid and excess
coupling elements which reside in regions outside of the negative
features on the surface.
2. The method of claim 1, wherein the negative features include a
depression, and wherein at least a portion of the depression has a
pyramidal shape.
3. The method of claim 1, wherein the coupling elements include
micro-spheres.
4. The method of claim 3, wherein the micro-spheres include a
metal, thereby facilitating electrical conduction via the
micro-spheres.
5. The method of claim 3, wherein the micro-spheres are transparent
in a range of wavelengths, thereby facilitating optical
communication via the micro-spheres.
6. The method of claim 1, wherein the geometry-based selection
involves selection based on sizes of at least some of the coupling
elements.
7. The method of claim 1, wherein the geometry-based selection
involves selection based on shapes of at least some of the coupling
elements.
8. The method of claim 1, wherein the chemical-based selection
involves selection based on a first compound coupled to at least
some of the coupling elements and a second compound coupled to at
least some of the negative features, and wherein the first compound
is configured to chemically bond to the second compound.
9. The method of claim 8, wherein a given compound, which can be
the first compound or the second compound, includes a nucleic
acid.
10. The method of claim 9, wherein the given compound includes a
compound selected from the group which includes: adenine, cytosine,
guanine, thymine, urasil, pseudouradine, thymidine, and
inosine.
11. The method of claim 8, wherein a given compound, which can be
the first compound or the second compound, includes a surfactant to
facilitate adhesion of at least some of the coupling elements to at
least some of the negative features.
12. The method of claim 1, wherein the fluidic assembly involves
mechanically agitating the fluid to facilitate the positioning.
13. The method of claim 1, wherein the positioning involves
electrostatically or magnetostatically driving at least some of the
coupling elements to the negative features.
14. The method of claim 1, wherein the assembling involves repeated
applications of fluids which include progressively smaller coupling
elements.
15. The method of claim 1, further comprising coupling a
semiconductor die to the base plate, wherein the coupling involves
aligning negative features on a first surface of the semiconductor
die with the coupling elements in the negative features on the
surface of the base plate.
16. The method of claim 15, wherein a pattern of the negative
features on the surface of the base plate determines an orientation
of the semiconductor die.
17. The method of claim 15, wherein the semiconductor die is
configured to communicate signals using proximity connectors
proximate to a second surface of the semiconductor die.
18. The method of claim 15, further comprising coupling another
semiconductor die to the semiconductor die using coupling elements
positioned in negative features on the second surface of the
semiconductor die and in negative features on a surface of the
other semiconductor die.
19. The method of claim 15, further comprising coupling a component
to the semiconductor die using coupling elements positioned in
negative features on the second surface of the semiconductor die
and in negative features on a surface of the component, wherein the
component is configured to couple signals from the semiconductor
die to another semiconductor die.
20. A method for assembling a multi-chip module (MCM), comprising:
applying a fluid to a surface of a base plate in the MCM, wherein
the fluid includes coupling elements, and wherein the coupling
elements include a first type of coupling element and a second type
of coupling element; positioning at least some of the coupling
elements into negative features on the surface of the base plate
using fluidic assembly, wherein a given coupling element in at
least some of the coupling elements selects a given negative
feature using chemical-based selection and geometry-based
selection, and wherein the first type of coupling elements have
different chemical-based and geometry-based selection than the
second type of coupling element; and removing the fluid and excess
coupling elements which reside in regions outside of the negative
features on the surface.
Description
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to techniques for assembling
systems containing semiconductor dies. More specifically, the
present invention relates to a method and an apparatus that
facilitate fluidic self-assembly of semiconductor dies in
multi-chip modules.
[0004] 2. Related Art
[0005] Advances in semiconductor technology presently make it
possible to integrate large-scale systems, which can include
hundreds of millions of transistors, into a single semiconductor
chip (or die). Integrating such large-scale systems onto a single
semiconductor chip increases the speed at which such systems can
operate, because signals between system components do not have to
cross chip boundaries, and are not subject to lengthy chip-to-chip
propagation delays. Moreover, integrating large-scale systems onto
a single semiconductor chip significantly reduces production costs,
because fewer semiconductor chips are required to perform a given
computational task.
[0006] Unfortunately, these advances in semiconductor technology
have not been matched by corresponding advances in inter-chip
communication technology. Semiconductor chips are typically
integrated onto a printed circuit board that contains multiple
layers of signal lines for inter-chip communication. However,
signal lines on a semiconductor chip are about 100 times more
densely packed than signal lines on a printed circuit board.
Consequently, only a tiny fraction of the signal lines on a
semiconductor chip can be routed across the printed circuit board
to other chips. This problem has created a bottleneck that
continues to grow as semiconductor integration densities continue
to increase.
[0007] Researchers have begun to investigate alternative techniques
for communicating between semiconductor chips. One promising
technique involves integrating arrays of capacitive transmitters
and receivers onto semiconductor chips to facilitate inter-chip
communication. If a first chip is situated face-to-face with a
second chip so that transmitter pads on the first chip are
capacitively coupled with receiver pads on the second chip, the
first chip can directly transmit signals to the second chip without
having to route the signals through intervening signal lines within
a printed circuit board.
[0008] Capacitive coupling requires precise alignment between the
transmitter pads and the receiver pads (which are more generally
referred to as proximity connectors), both in a plane defined by
the pads and in a direction perpendicular to the plane.
Misalignment between the transmitter pads and the receiver pads may
cause each receiving pad to span two transmitting pads, thereby
destroying a received signal. In theory, for communication to be
possible, chips must be aligned so that misalignment is less than
half of a pitch between the pads. In practice, the alignment
requirements may be more stringent. In addition, reducing
misalignment can improve communication performance between the
chips and reduce power consumption.
[0009] Unfortunately, it can be very challenging to align chips
properly. Existing approaches include mechanical mounting
structures that facilitate self-alignment and/or self-adjustment of
pad positions. FIG. 1 illustrates one such approach in which
negative features, such as etch pits 112, and micro-spheres 114 are
used to align semiconductor dies 110 (and thus proximity
connectors) in a multi-chip module (MCM). These etch-pits can be
defined photolithographically using a subtractive process (i.e., a
photolithographic process that removes material), which takes place
before, during, or after circuit fabrication on the semiconductor
dies 110. This enables the etch pits 112 to be accurately placed on
the semiconductor dies 110 in relationship to circuits and the
proximity connectors. Therefore, the photolithographic alignment
between the etch pits 112 and circuits establishes precise
alignment between circuits on the top and bottom semiconductor dies
110.
[0010] Note that the alignment in the X, Y, and Z directions, as
well as the angular alignment between semiconductor dies 110,
depends only on the relative sizes of the etch-pits 112 and the
micro-spheres 114, and on the orientation and placement of the etch
pits 112 on the semiconductor dies 110. In particular, the lateral
alignment between circuits on the semiconductor dies 110 is
achieved in a `snap-fit` manner, provided the micro-spheres 114 are
appropriately sized to fit into the etched pits 112. Clearly,
micro-spheres 114 that are too large do not fit into the etch pits
112, and micro-spheres 114 that are too small do not properly align
the top and bottom semiconductor dies 110. However, if the
micro-spheres 114 sit in the groove of the etch pits 112 correctly
(for example, their equators lie exactly at or higher than the
surface of the semiconductor die 110-1 and exactly at or lower than
the surface of semiconductor die 110-2) then circuits on the top
and bottom semiconductor dies 110 are precisely aligned. Similarly,
alignment in the Z direction is a function of the photolithographic
feature size of the etch pits 112, the etch depth of the etch pits
112, and the diameter of the micro-spheres 114.
[0011] While this approach is useful and applicable to packaging
and assembly of MCMs that include two or more semiconductor dies
110, it suffers from the limitation that the placement of
micro-spheres 114 into the etch-pits 112 is not a parallel,
wafer-scale process that can be readily performed at a foundry.
Instead, the micro-spheres 114 are often placed into individual
semiconductor dies 110 after fabrication. Consequently, this
approach may add complexity and cost to the process of assembling
MCMs.
[0012] Hence, what is needed is a method and an apparatus that
facilitates aligning proximity connectors without the problems
listed above.
SUMMARY
[0013] One embodiment of the present invention provides a method
for assembling a multi-chip module (MCM). During this method, a
fluid that includes coupling elements is applied to a surface of a
base plate in the MCM. Then, at least some of the coupling elements
are positioned into negative features on the surface of the base
plate using fluidic assembly. Note that a given coupling element
selects a given negative feature using chemical-based selection
and/or geometry-based selection. Next, the fluid and excess
coupling elements (which reside in regions outside of the negative
features on the surface) are removed.
[0014] In some embodiments, the negative features include a
depression, and at least a portion of the depression has a
pyramidal shape.
[0015] In some embodiments, include micro-spheres. These
micro-spheres may include a metal, thereby facilitating electrical
conduction via the micro-spheres. Moreover, in some embodiments the
micro-spheres are transparent in a range of wavelengths, thereby
facilitating optical communication via the micro-spheres.
[0016] In some embodiments, the geometry-based selection involves
selection based on sizes and/or shapes of at least some of the
coupling elements.
[0017] In some embodiments, the chemical-based selection involves
selection based on a first compound coupled to at least some of the
coupling elements and a second compound coupled to at least some of
the negative features. Note that the first compound is configured
to chemically bond to the second compound. In some embodiments, a
given compound, which can be the first compound or the second
compound, includes a nucleic acid, such as: adenine, cytosine,
guanine, thymine, urasil, pseudouradine, thymidine, and/or inosine.
Furthermore, in some embodiments the given compound includes a
surfactant to facilitate adhesion of at least some of the coupling
elements to at least some of the negative features.
[0018] In some embodiments, the fluidic assembly involves
mechanically agitating the fluid to facilitate the positioning.
Moreover, in some embodiments the positioning involves
electrostatically and/or magnetostatically driving at least some of
the coupling elements to the negative features.
[0019] In some embodiments, the assembling involves repeated
applications of fluids which include progressively smaller coupling
elements.
[0020] In some embodiments, the method further includes coupling a
semiconductor die to the base plate, where the coupling involves
aligning negative features on a first surface of the semiconductor
die with the coupling elements in the negative features on the
surface of the base plate. Note that a pattern of the negative
features on the surface of the base plate may determine an
orientation of the semiconductor die. Also note that the
semiconductor die is configured to communicate signals using
proximity connectors proximate to a second surface of the
semiconductor die.
[0021] In some embodiments, the method further includes coupling
another semiconductor die to the semiconductor die using coupling
elements positioned in negative features on the second surface of
the semiconductor die and in negative features on a surface of the
other semiconductor die. Moreover, in some embodiments the method
further includes coupling a component to the semiconductor die
using coupling elements positioned in negative features on the
second surface of the semiconductor die and in negative features on
a surface of the component. Note that the component is configured
to couple signals from the semiconductor die to another
semiconductor die.
[0022] Another embodiment of the present invention provides another
method for assembling MCMs. During this method, the applied fluid
includes a first type of coupling element and a second type of
coupling element. Furthermore, the first type of coupling elements
have different chemical-based and/or geometry-based selection than
the second type of coupling element.
BRIEF DESCRIPTION OF THE FIGURES
[0023] FIG. 1 is a block diagram illustrating an existing
multi-chip module (MCM).
[0024] FIG. 2 is a block diagram illustrating a device that
includes proximity connectors in accordance with an embodiment of
the present invention.
[0025] FIG. 3 is a block diagram illustrating an MCM that includes
semiconductor dies that communicate using proximity communication
in accordance with an embodiment of the present invention.
[0026] FIG. 4A is a block diagram illustrating a semiconductor die
in accordance with an embodiment of the present invention.
[0027] FIG. 4B is a block diagram illustrating a semiconductor die
in accordance with an embodiment of the present invention.
[0028] FIG. 4C is a block diagram illustrating a semiconductor die
in accordance with an embodiment of the present invention.
[0029] FIG. 5 is a block diagram illustrating a semiconductor die
in accordance with an embodiment of the present invention.
[0030] FIG. 6 is a block diagram illustrating a base plate in
accordance with an embodiment of the present invention.
[0031] FIG. 7 is a block diagram illustrating a technique for
assembling an MCM in accordance with an embodiment of the present
invention.
[0032] FIG. 8 is a flow chart illustrating a process for assembling
an MCM in accordance with an embodiment of the present
invention.
[0033] FIG. 9 is a flow chart illustrating a process for assembling
an MCM in accordance with an embodiment of the present
invention.
[0034] FIG. 10 is a block diagram illustrating a computer system in
accordance with an embodiment of the present invention.
[0035] Note that like reference numerals refer to corresponding
parts throughout the drawings.
DETAILED DESCRIPTION
[0036] The following description is presented to enable any person
skilled in the art to make and use the invention, and is provided
in the context of a particular application and its requirements.
Various modifications to the disclosed embodiments will be readily
apparent to those skilled in the art, and the general principles
defined herein may be applied to other embodiments and applications
without departing from the spirit and scope of the present
invention. Thus, the present invention is not intended to be
limited to the embodiments shown, but is to be accorded the widest
scope consistent with the principles and features disclosed
herein.
[0037] Embodiments of a method, a semiconductor die, an MCM, and
systems that include the MCM are described. Note that the MCM,
which is sometimes referred to as a macro-chip, includes an array
of chip modules (CMs) or single-chip modules (SCMs), and a given
SCM includes at least one semiconductor die. Furthermore, the
semiconductor die communicates with other semiconductor dies, SCMs,
and/or devices in the MCM using proximity communication of
electrical (capacitively coupled) signals and/or proximity
communication of optical signals (which are, respectively,
sometimes referred to as electrical proximity communication and
optical proximity communication). This proximity communication
occurs via proximity pads or connectors that are located on or are
proximate to a surface of the semiconductor die.
[0038] Alignment of proximity connectors on neighboring or adjacent
semiconductor dies or components is facilitated by features on one
or more surface of the semiconductor dies. For a given
semiconductor die, these features may include positive features
(which protrude or extend above a surrounding region) and/or
negative features (which are positioned below or recessed relative
to a surrounding region). Note that the features may be defined
using an additive (i.e., a material-deposition) and/or a
subtractive (i.e., a material-removal) processes. In some
embodiments, features on a first semiconductor die mate with or
couple to features on a second semiconductor die. Furthermore, in
some embodiments positive and/or negative features (such as a
pyramidal-shaped etch pit or slot) are used in combination with
inter-chip coupling elements (such as micro-spheres or balls). For
example, the micro-spheres may be used to align components and/or
to couple power or optical signals to the semiconductor die.
[0039] During the method, fabrication of the MCM involves fluidic
self-assembly of the semiconductor dies, SCMs, and/or components.
In particular, one or more types of coupling elements may be
positioned into features in a portion of the MCM (such as abase
plate and/or a semiconductor die) using chemical-based and/or
geometry-based selection. For example, the geometry-based selection
may involve selection based on sizes and/or shapes of at least some
of the coupling elements. Furthermore, the chemical-based selection
may involve chemical bonding (such as ionic, covalent, permanent
dipole, and/or van der Waals) of at least some of the coupling
elements to at least some of the features. This bonding may be
between compounds that include nucleic acids (such as
deoxyribonucleic acid or DNA). In some embodiments, the fluidic
assembly involves: mechanical agitation, an electrostatic driving
force, and/or a magnetostatic driving force. Note that this
technique for assembling the MCM can be implemented in a
wafer-scale process, thereby facilitating: simpler assembly, rapid
assembly (for example, in parallel), and/or lower cost.
[0040] Embodiments of the semiconductor die and/or the MCM may be
used in a variety of applications, including: telephony, storage
area networks, data centers, networks (such as local area
networks), and/or computer systems (such as multi-processor
computer systems). For example, the semiconductor die may be
included in a switch in a backplane that is coupled to multiple
processor blades, or in a switch that is coupled to different types
of components (such as processors, memory, I/O devices, and/or
peripheral devices).
[0041] We now describe embodiments of a semiconductor die and an
MCM. FIG. 2 presents a block diagram illustrating an embodiment of
a device 200 that includes proximity connectors 212 (which may be
capacitive, optical, inductive, and/or conductive-based
connectors). Device 200 may include at least one semiconductor die
210, where semiconductor die 210 may include integrated circuit
electronics corresponding to layers deposited on a semiconductor
substrate. Note that semiconductor die 210 may be packaged in an
SCM and/or an MCM, where the MCM may include two or more SCMs. When
packaged, for example in the SCM or the MCM, semiconductor die 210
is sometimes referred to as a "chip."
[0042] In one embodiment, the proximity connectors 212 may be
located on or proximate to at least one surface of the
semiconductor die 210, the SCM and/or the MCM. In other
embodiments, the semiconductor die 210, the SCM and/or the MCM may
be coupled to the proximity connectors 212. In an exemplary
embodiment, the proximity connectors 212 are substantially located
at or near one or more corners (proximity connectors 212-1 and
212-2) and/or edges (proximity connectors 212-3) of the
semiconductor die 210. In other embodiments, proximity connectors
212 may be situated at one or more arbitrary locations on, or
proximate to, the surface of the semiconductor die 210.
[0043] As illustrated for the proximity connectors 212-1, there is
a first pitch 214-1 between adjacent connectors or pads in a first
direction (X) 216 of the surface and a second pitch 214-2 between
adjacent connectors or pads in a second direction (Y) 218 of the
surface. In some embodiments, the first pitch 214-1 and the second
pitch 214-2 are approximately equal.
[0044] FIG. 3 presents a block diagram illustrating an embodiment
of an MCM 300 that includes semiconductor dies 210 that communicate
using capacitively coupled proximity communication (which is used
as an illustration). Semiconductor dies 210 may include proximity
connectors or pads 212 that are located on or proximate to at least
surfaces 308 of the semiconductor dies 210. For example, the
proximity connectors 212 may be situated beneath protective layers
such that they are located below the surfaces 308. Moreover,
subsets of the proximity connectors 212 may be coupled to transmit
circuits 310 (such as transmit drivers) and receive circuits 312
(such as receivers). One of the transmit circuits 310, at least a
subset of the proximity connectors 212 on the adjacent
semiconductor dies 210, and one of the receive circuits 312 may
constitute a communication channel. For example, the communication
channel may include: transmit circuit 310-1, some of the proximity
connectors 212, and receive circuit 312-1. Note that transmit
circuits 310 and receive circuits 312 may utilize voltage-mode
signaling (i.e., voltage-mode drivers and receivers). Furthermore,
semiconductor dies 210 may also include wiring and electronics (not
shown) to relay the data signals to additional electronics on the
semiconductor dies 210, such as: logic, memory (for example, a
packet buffer memory), I/O ports, demultiplexers, multiplexers,
and/or switching elements.
[0045] In order to communicate data signals using proximity
communication, transmit and receive proximity connectors 212 on
adjacent semiconductor dies 210 may have, at worst, only limited
misalignment, i.e., substantially accurate alignment. For densely
packed proximity connectors, i.e., proximity connectors 212 having
a small spacing or pitch 214 (FIG. 2) between adjacent pads, the
alignment between two or more proximity connectors 212 on adjacent
semiconductor dies 210 may be within a few microns in the first
direction (X) 216 (FIG. 2) and/or a few microns in the second
direction (Y) 218 (FIG. 2), where the first direction (X) 216 and
the second direction (Y) 218 are in a first plane including at
least some of the proximity connectors 212. The alignment may be
within a few microns in a third direction (Z) approximately
perpendicular to the first plane. Note that MCM 300 illustrates a
misalignment 314 in the third direction (Z).
[0046] In some embodiments, the proximity connectors 212 may be
aligned in all six degrees of freedom, including: the first
direction (X) 216 (FIG. 2); the second direction (Y) 218 (FIG. 2);
the third direction (Z); an angle in the first plane defined by the
first direction (X) 216 (FIG. 2) and the second direction (Y) 218
(FIG. 2); an angle in a second plane defined by the first direction
(X) 216 (FIG. 2) and the third direction (Z); and an angle in a
third plane defined by the second direction (Y) 218 (FIG. 2) and
the third direction (Z). Note that X 216, Y 218, and Z are the
normal orthogonal axes of 3-space. Also note that if a surface,
such as the surface 308-1, of either of the adjacent semiconductor
dies 210 is non-planar (for example, due to quadrapole distortion),
additional alignment problems may be introduced.
[0047] In some embodiments, allowed misalignment in the first
direction (X) 216 (FIG. 2), the second direction (Y) 218 (FIG. 2),
and/or the third direction (Z) is less than one half of the pitch
214 (FIG. 2) between adjacent pads 212. For example, misalignment
in the first direction (X) 216 (FIG. 2) and/or the second direction
(Y) 218 (FIG. 2) may be less than 25 .mu.m, and the misalignment
314 in the third direction (Z) may be less than 5 .mu.m. In some
embodiments, the misalignment 314 is between 1 and 10 .mu.m.
[0048] Solutions, such as self-aligning and/or self-adjusting of
the relative positions of the proximity connectors 212 on adjacent
semiconductor dies 210 (and/or in a component such as a bridge chip
coupling two or more semiconductor dies 210) may reduce and/or
eliminate the misalignment 314 in the third direction (Z). For
example, structures that have flexibility compliance (or are
spring-like) may be used. In other embodiments, a feedback control
loop may be used to reduce and/or eliminate the misalignment 314 in
the third direction (Z). Moreover, as discussed further below,
alignment of the semiconductor dies 210 (and thus, at least some of
the proximity connectors 212) may be facilitated by coupling
alignment features 316 located on or proximate to the surfaces
308.
[0049] Reducing or eliminating the misalignment 314, in turn, may
lead to at least partial overlap of one or more proximity
connectors 212 on the adjacent semiconductor dies 210 and may
therefore increase a magnitude of the capacitively coupled data
signals. In addition, the solutions may reduce misalignment in the
first plane, i.e., the plane including at least some of the
proximity connectors 212, when used in conjunction with techniques
such as electronic steering (where data signals are routed to given
proximity connectors 212 based on the alignment in the first
plane). Consequently, these solutions may facilitate proximity
communication between the semiconductor dies 210, SCMs and/or MCMs.
The solutions may also reduce and/or eliminate a need for narrow
tolerances, precise manufacturing, and/or precise assembly of the
semiconductor dies 210, the SCM and/or the MCM.
[0050] In the embodiments described above and below, the proximity
connectors 212 on the adjacent semiconductor dies 210 utilize
capacitive coupling for inter-chip communication. In other
embodiments, different connectors may be overlapped on adjacent
semiconductor dies 210. For example, one embodiment of the present
invention uses optical proximity connectors, in which data signals
are communicated optically between terminals on adjacent
semiconductor dies 210. Moreover, optical waveguides, fibers, light
sources (such as diodes or lasers), and/or transceivers may be
integrated onto semiconductor dies 210 (or an accompanying circuit
board) for intra-chip communication. Other embodiments use magnetic
proximity connectors, in which data signals are communicated
magnetically between terminals on closely adjacent semiconductor
dies 210, or conductive connectors (such as an array of solder
balls).
[0051] In some embodiments, semiconductor dies 210 are contained in
an array of semiconductor dies in an MCM. For example, as
illustrated in FIG. 3, semiconductor dies 210 in such an array may
be positioned face-to-face, such that proximity connectors 212 on
the corners (and more generally on side edges) of the semiconductor
dies 210 overlap and couple signals between adjacent semiconductor
dies using, for example, capacitively coupled proximity
communication. In another embodiment, the semiconductor dies 210
are face up (or face down) and signals between adjacent
semiconductor dies are capacitively coupled via a face-down (or
face-up) bridge chip.
[0052] While the device 200 (FIG. 2) and the MCM 300 are
illustrated as having a number of components in a given
configuration, in other embodiments the device 200 (FIG. 2) and/or
the MCM 300 may include fewer components or additional components,
two or more components may be combined into a single component,
and/or a position of one or more components may be changed.
Furthermore, functions of the MCM 300 may be implemented in
hardware and/or in software.
[0053] We now described embodiments of alignment features, such as
alignment features 316. In general, a wide variety of features,
including positive features and negative features, may be used.
These features may be fabricated on a wide variety of materials,
including a semiconductor, a metal, a glass, sapphire, and/or
silicon dioxide. In the discussion that follows silicon is used as
an illustrative example. Furthermore, the features may be
fabricated using additive and/or subtractive processes, including
sputtering, isotropic etching, and/or anisotropic etching. In some
embodiments, features are defined using photolithographic and/or
direct-write techniques.
[0054] FIGS. 4A-4C provide embodiments 400, 430, and 450 that
illustrate negative features fabricated on semiconductor dies 410,
including: trenches, etch pits or slots 412, pyramids 440, and/or
truncated pyramids 460. As noted previously, negative features may
be fabricated using a subtractive process, for example, by
selective etching into a silicon substrate. Note that the etching
may be self-limiting or self-terminating, such as anisotropic
lithography along the <111> crystallographic direction to
produce pyramids 440 (FIG. 4B). However, in some embodiments etch
stops are defined, for example, using CMOS technology, to produce
truncated pyramids 460 (in which the sides are along the
<111> crystallographic direction and the bottom is, for
example, along the <100> crystallographic direction).
Alternatively, truncated pyramids 460 may be fabricated by stopping
an anisotropic etch prior to completion (such as when a desired
etch depth is reached).
[0055] While not shown, positive features may include: hemispheres,
ridges, top-hat shapes or bumps, pyramids, and/or truncated
pyramids. For example, photoresist or metal bumps may be
lithographically defined and annealed to allow surface tension to
draw the material into a hemisphere (which may be subsequently hard
baked). In some embodiments, these features mate with or couple to
corresponding negative features facilitating `snap-fit` assembly,
thereby providing and maintaining precise alignment.
[0056] While embodiments 400 (FIG. 4A), 430 (FIG. 4B), and 450 (and
the embodiments described below) are illustrated as having a
limited number of negative features having a given configuration,
other embodiments may include fewer components or additional
components, two or more components may be combined into a single
component, and/or a position of one or more components may be
changed. For example, the negative and/or positive features may be
fabricated in one or more directions. Thus, in some embodiments,
positive features such as hemispheres have a
hexagonal-closed-packed configuration. Furthermore, a wide variety
of materials may be used for the positive and/or negative features.
And in some embodiments, a given semiconductor die includes both
positive and negative features, thereby breaking the symmetry and
ensuring that chips can only be assembled in one physical
arrangement or orientation
[0057] In some embodiments, a shape of one or more positive and/or
a negative features is used to determine an orientation of a
semiconductor die or to limit the possible semiconductor dies that
a given semiconductor die can mate with in an MCM (thereby
facilitating self-assembly of an MCM). This is illustrated in FIG.
5, which provides a block diagram of an embodiment 500 of a
semiconductor die 510 that includes a key-shaped feature 512.
Moreover, in some embodiments an arrangement of one or more
features is used to restrict orientation or mating of semiconductor
dies. This is illustrated in FIG. 6, which provides a block diagram
of an embodiment 600 of a base plate 610 and features 612. Note
that semiconductor dies and/or components (such as bridge chips)
couple to the base plate 610 during the assembly of an MCM.
[0058] In some embodiments, one or more features on the
semiconductor dies include a material, such as a soft metal to
provide stress relief (for example, for stress due to relative
motion or due to temperature differences) between coupled
semiconductor dies. Furthermore, metal layers in or on such
features may also allow coupling elements (such as micro-spheres)
in an MCM to couple power to one or more semiconductor dies. In
these embodiments, the coupling elements are made of metal or have
a metal (conductive) coating. These coupling elements may or may
not be used to align the semiconductor dies. For example, in some
embodiments alignment is facilitated using positive and negative
features and micro-spheres are used to couple power and/or ground
to the semiconductor dies.
[0059] In some embodiments, spherical lenses or micro-spheres are
used to align semiconductor dies and/or to couple optical signals
between semiconductor dies. For example, micro-spheres may image
light from a waveguide integrated on a first semiconductor die onto
a waveguide integrated on a second semiconductor die, thereby
facilitating optical communication between these semiconductor
dies. In another embodiment, spherical resonators doped with
optional optical gain materials are used to precisely align the
first semiconductor die to the second semiconductor die. These
spherical resonators may facilitate azimuthal coupling between the
first waveguide integrated on the first semiconductor die and the
second waveguide integrated on the second semiconductor die.
Moreover, the spherical resonators may facilitate optical filtering
and optical gain during optical communication between these
semiconductor dies.
[0060] Thus, the micro-spheres may include materials such as:
sapphire, glass, silicon dioxide, conductive materials (for
example, a metal), and/or non-conductive materials.
[0061] In the discussion that follows, coupling elements (such as
micro-spheres) are used in conjunction with negative features (as
an example) to align semiconductor dies in an MCM. As noted
previously, it is often difficult to place the coupling elements
into the features during a wafer-scale process. In principle,
fluidic self-assembly may be used to sort and position objects,
such as coupling elements, into the features during a wafer-scale
process. For example, assembly may be based on the geometry (i.e.,
the size, shape, and/or orientation) of the coupling elements
and/or the features. However, while such geometry-based techniques
offer high directional selectivity (as illustrated in FIGS. 5 and
6), the site selectivity (i.e., the ability to ensure that a given
type of coupling element is placed into or coupled to a given type
of feature) may be limited. This is a challenge, especially in
heterogeneous environments that include coupling elements and/or
features that have a range of: sizes, shapes, and/or
orientations.
[0062] In contrast, chemical-based coatings (for example, adhesion
promoters such as surfactants) on the coupling elements and/or in
the features can offer high site selectivity. While arbitrary
chemical compounds may be used to implement chemical-based fluidic
self-assembly, in the discussion that follows chemicals containing
one or more nucleic acids or nucleotides (such as DNA) are used as
an illustrative example.
[0063] Nucleotides are composed of a phosphodiester covalently
bound to a nucleoside or a derivative of a deoxyribose sugar and
either a purine or pyrimidine nucleobase. Nucleobases include
purines, such as: adenine (A), guanine (G), and the pyrimidines,
i.e., thymine (T) and cytosine (C). These nucleotides can be bound
to each other to form a linear chain (or strand) through their
phosphodiester bonds that must terminate or begin at either the 5'
or 3' carbon of the adjacent nucleotide (i.e., the 5.sup.th or
3.sup.rd carbon in the deoxyribose sugar). This arrangement imparts
a direction to the chain because of an exposed 3' or 5' site at
opposite ends. Note that each end is capped with either an --OH or
a phosphate group.
[0064] A sequence of nucleotides (also called bases) in the strand
can be arbitrary and by convention is written as a sequence from
the 5' end to the 3' end (for example, 5'-AGGTC-3'). This
represents a so-called single-stranded DNA molecule. Furthermore,
the geometry of the phosphodiester bond and the shape of the
nucleosides create the potential for single strands of DNA to wrap
around one another in anti-parallel directions. Thus, any two
strands are geometrically compatible if oriented in an
anti-parallel fashion and can form a helical structure, or a
double-stranded DNA molecule.
[0065] DNA-assisted self-assembly is a technique in which
artificially synthesized single-stranded DNA self-assemble into DNA
molecules. These DNA molecules have ends that display strong
affinity for and preferentially match to the corresponding ends of
certain other DNA molecules, thereby promoting the matching or
mating of the molecules into a lattice. Note that the self-assembly
of large two-dimensional lattices consisting of thousands of
molecules has been demonstrated, and even three-dimensional
lattices are expected. This spontaneous self-ordering of
sub-structures into super-structures can be a powerful tool for
self-assembly of complex systems.
[0066] An important quality of DNA that makes suitable for
self-assembly is its ability to hybridize with its complement with
very high selectivity. Furthermore, the ability to convert
double-stranded DNA into a highly conductive ohmic contact during a
metallization process makes the use of DNA assembly at micro- and
nano-length scales useful for establishing circuit connections.
Note that the hybridization or self-assembly is guided by the
thermodynamic properties of DNA that give it the ability to form
unique pairs among complementary strands. Also note that these
techniques may be used to create self-assembling structures at
length scales between 10 nm (the molecular scale) and a few
centimeters with strong site selectivity. For example, simple
experiments have shown that conductive gold balls can be hybridized
using DNA to select specific locations on an array.
[0067] Unfortunately, there are some problems associated with
DNA-assisted self-assembly. In particular, self-assembly of
nano-scale components may be hindered by surface-area effects that
limit the yield of the process. In other words, there may be
competing nonspecific interactions that need to be reduced in order
to enhance specific (for example, DNA-binding) assembly events. In
addition, the assembly of DNA molecules accelerates inversely with
temperature. Consequently, DNA-assisted self-assembly is an
inherently stochastic process with potentially uncertain result and
the termination of such a process is not guaranteed.
[0068] These problems (and those discussed previously) may be
addressed by combining geometry-based selection and chemical-based
selection during fluidic self-assembly to provide high site
selection. In some embodiments, a highly selective, stochastic
assembly process (such as DNA-assisted self-assembly) includes a
strong homogeneous forcing function. This assembly process is rapid
and parallel (thus, reducing assembly time and cost), and
facilitates selective placement of alignment microstructures (i.e.,
coupling elements) into corresponding features (such as etch pits)
in the host semiconductor dies and/or other components in an MCM
(such as the base plate or bridge chips). In addition, the
combination of these techniques helps terminate the assembly
process with high yield and is well suited for heterogeneous
assembly.
[0069] FIG. 7 presents a block diagram illustrating an embodiment
700 of a technique for assembling an MCM in which micro-spheres 716
are placed into corresponding pyramidal-shaped features 712 in a
base plate 710. In this embodiment, the pyramidal-shaped features
712 include chemical coatings 714 and the micro-spheres 716 include
chemical coatings 718. These coatings provide chemical-based
selectivity. Furthermore, the geometry of the micro-spheres 716
and/or the pyramidal-shaped features 712 provides geometry-based
selectivity, as illustrated by the different sizes of the
micro-spheres 716 and the pyramidal-shaped features 712 (thus,
micro-sphere 716-1 may be positioned into pyramidal-shaped features
712-1 and micro-sphere 716-2 may be positioned into
pyramidal-shaped features 712-2). Using this assembly technique,
alignment micro-structures or coupling elements (such as the
micro-spheres 716) can be self-assembled into the appropriate
pyramidal-shaped features 712 in the base plate 710 (such as a
silicon chip) with high accuracy and yield. Note that these
coupling elements may have: differing purposes, materials, sizes,
and/or shapes.
[0070] In an exemplary embodiment, coatings 714 and/or 718 include
one or more nucleic acids or nucleotides, i.e., DNA-assisted
fluidic self-assembly is used to position the micro-spheres 716
into the pyramidal-shaped features 712. This may be accomplished by
coating a set of micro-structures (such as at least some of the
micro-spheres 716) with a first type of artificially produced DNA
strands (i.e., at least some of the coatings 718). Then, a
photolithographic mask may be used to place a second set of DNA
strands (i.e., at least some of the coatings 714), which are
complementary to the first type of DNA strands and have a high
affinity for the first type of DNA strands, into a corresponding
set of target features (i.e., at least some of the pyramidal-shaped
features 712) in the base plate 710 where the set of
micro-structures are to be assembled.
[0071] In some embodiments, these operations are repeated and
multiple types of pairs of coatings are used. For example, a second
set of micro-structures are coated with a third type of
artificially produced DNA strands and another photolithographic
mask may be used to place a fourth type of artificially produced
DNA strands into a corresponding set of target features. Note that
the third and fourth types of artificially produced DNA strands
have a high affinity for each other and may also have a strong
repulsion with the first and second types of artificially produced
DNA strands. These operations may be repeated until all of the
micro-spheres 716 and all of the pyramidal-shaped features 712
include coatings 714 and 718.
[0072] In some embodiments of the assembly process, fluids
containing different micro-spheres 716 (i.e., having different
sizes, shapes, and/or coatings 718) may be applied sequentially.
For example, a first fluid (such as a solvent) containing larger
micro-spheres, micro-spheres having a given shape (such as a
cylinder or a sphere), and/or micro-spheres having a first type of
coating may be applied to the base plate 710. This fluid may remain
in contact with the base plate 710 for sufficient time (for
example, a few minutes) to allow these micro-spheres to couple to
corresponding pyramidal-shaped features 712. Then, the fluid may be
removed and any residual or excess micro-spheres, which are on the
surface of the base plate 710 but which are not in or chemically
bonded to appropriate pyramidal-shaped features 712, may be
removed. For example, the fluid may be removed by evaporation and
residual micro-spheres may be removed using a rise or wash
operation. Next, these operations may be repeated with one or more
additional fluids containing progressively smaller micro-spheres,
micro-spheres having another shape, and/or micro-spheres having
different types of coatings. Alternatively, in some embodiments the
multiple types of micro-spheres are applied to the base plate 710
in parallel, i.e., using a single fluid.
[0073] Note that various metrics may be used to determine how long
a given fluid needs to be in contact with the base plate 710. For
example, contact may be maintained until a percentage or all of the
pyramidal-shaped features 712 are filled with micro-spheres 716. In
some embodiments, a fill factor is determined by measuring how many
of the pyramidal-shaped features 712 appear as light or dark in an
image.
[0074] In some embodiments, at least some of the micro-spheres 716
are dissolved after assembly of the MCM is completed. For example,
some of the micro-spheres 716 may include polystyrene, which may be
dissolved using acetone or another organic solvent. Moreover, in
some embodiments extra micro-spheres are recovered or recycled from
one or more fluids using a filtering operation.
[0075] In some embodiments, a driving force is used to accelerate
the fluidic assembly. For example, an optional driver 720 may apply
a DC or time varying field between a terminal 722 and the base
plate 710. In some embodiments, the driving force includes:
mechanical agitation (such as ultrasound), an electric field, a
magnetic field, and/or an electromagnetic field. Moreover, in some
embodiments gravity is used to separate bound micro-spheres from
excess micro-spheres, which may simply roll of the surface of a
tilted base plate 710. Note that the use of a driving force can
reduce a sensitivity of the fluidic self-assembly process to
temperature variations and/or surface tension.
[0076] In an exemplary embodiment, the driving force is an electric
field, in an electrochemical transport process referred to as
micro-electrophoresis. However, this technique is only applicable
to non-conductive, homogeneous coupling elements (such as glass
micro-spheres) and movement is only restricted along specific
directions (i.e., along the direction of the applied electric
field).
[0077] Using one or more of these embodiments, an MCM may be
assembled with high accuracy and high site selectivity. In
addition, by combining geometry-based selectivity with
chemical-based selectivity, a stochastic process (such as DNA-based
fluidic self-assembly) may be converted into one with a known, high
yield.
[0078] We now describe embodiments of methods for assembling an
MCM. FIG. 8 provides a flow chart illustrating a process 800 for
assembling an MCM. During this process, a fluid that includes
coupling elements is applied to a surface of a base plate in an MCM
(810). Then, at least some of the coupling elements are positioned
into negative features on the surface of the base plate using
fluidic assembly (812). Note that a given coupling element selects
a given negative feature using chemical-based selection and/or
geometry-based selection. Next, the fluid and excess coupling
elements (which reside in regions outside of the negative features
on the surface) are removed (814).
[0079] FIG. 9 provides a flow chart illustrating a process 900 for
assembling an MCM. During this process, a fluid that includes
coupling elements is applied to a surface of a base plate in an MCM
(910). This fluid contains a first type of coupling elements and a
second type of coupling elements. Then, at least some of the
coupling elements are positioned into negative features on the
surface of the base plate using fluidic assembly (912). Note that a
given coupling element selects a given negative feature using
chemical-based selection and/or geometry-based selection.
Furthermore, the first type of coupling elements have different
chemical-based selection and/or different geometry-based selection
than the second type of coupling elements. Next, the fluid and
excess coupling elements (which reside in regions outside of the
negative features on the surface) are removed (814).
[0080] In some embodiments of the processes 800 (FIG. 8) and/or 900
there may be additional or fewer operations, the order of the
operations may be changed, and two or more operations may be
combined into a single operation.
[0081] Note that the present invention may be used to fabricate
MCMs that are included in systems. For example, FIG. 10 presents a
block diagram illustrating an embodiment of a computer system 1000,
which includes one or more processors 1010, a communication
interface 1012, a user interface 1014, and one or more signal lines
1022 coupling these components together. Note that the one or more
processing units 1010 may support parallel processing and/or
multi-threaded operation, the communication interface 1012 may have
a persistent communication connection, and the one or more signal
lines 1022 may constitute a communication bus. Moreover, the user
interface 1014 may include: a display 1016, a keyboard 1018, and/or
a pointer, such as a mouse 1020.
[0082] Computer system 1000 may include memory 1024, which may
include high speed random access memory and/or non-volatile memory.
More specifically, memory 1024 may include: ROM, RAM, EPROM,
EEPROM, FLASH, one or more smart cards, one or more magnetic disc
storage devices, and/or one or more optical storage devices. Memory
1024 may store an operating system 1026, such as SOLARIS, LINUX,
UNIX, OS X, or WINDOWS, that includes procedures (or a set of
instructions) for handling various basic system services for
performing hardware dependent tasks. Memory 1024 may also store
procedures (or a set of instructions) in a communication module
1028. The communication procedures may be used for communicating
with one or more computers and/or servers, including computers
and/or servers that are remotely located with respect to the
computer system 1000.
[0083] Memory 1024 may also include the one or more program modules
(of sets of instructions) 1030. Instructions in the program modules
1030 in the memory 1024 may be implemented in a high-level
procedural language, an object-oriented programming language,
and/or in an assembly or machine language. The programming language
may be compiled or interpreted, i.e., configurable or configured to
be executed by the one or more processing units 1010.
[0084] Computer system 1000 may include one or more macro-chips
1008 (such as one or more MCMs) that include semiconductor dies
and/or components that are aligned using an assembly process that
involves chemical-based and/or geometry-based selection as
described in the previous embodiments.
[0085] Computer system 1000 may include fewer components or
additional components, two or more components may be combined into
a single component, and/or a position of one or more components may
be changed. In some embodiments, the functionality of the computer
system 1000 may be implemented more in hardware and less in
software, or less in hardware and more in software, as is known in
the art.
[0086] Although the computer system 1000 is illustrated as having a
number of discrete items, FIG. 10 is intended to be a functional
description of the various features that may be present in the
computer system 1000 rather than as a structural schematic of the
embodiments described herein. In practice, and as recognized by
those of ordinary skill in the art, the functions of the computer
system 1000 may be distributed over a large number of servers or
computers, with various groups of the servers or computers
performing particular subsets of the functions. In some
embodiments, some or all of the functionality of the computer
system 1000 may be implemented in one or more application specific
integrated circuits (ASICs) and/or one or more digital signal
processors (DSPs).
[0087] The foregoing descriptions of embodiments of the present
invention have been presented for purposes of illustration and
description only. They are not intended to be exhaustive or to
limit the present invention to the forms disclosed. Accordingly,
many modifications and variations will be apparent to practitioners
skilled in the art. Additionally, the above disclosure is not
intended to limit the present invention. The scope of the present
invention is defined by the appended claims.
* * * * *